This invention relates to a method for preparing a hydrodesulfurization catalyst.
It is well known and has been practiced to carry out desulfurization by making sulfur-containing hydrocarbons and hydrogen come into contact with a catalyst comprising alumina having metals of VIB Group and VIII Group of the Periodic Table supported thereon under a pressure of 7-200 atm at a temperature of about 100.degree.-450.degree. C., thereby hydrogenating the sulfur compound but without hydrogenating the raw material fraction. Each conventional catalyst produces a good result in its own way, but various studies have been actively continued in order to develop a catalyst having a better activity and various proposals have been made with regard to hydrodesulfurization catalysts, usage thereof and methods of preparation thereof.
Prior to the present invention, Japanese Patent Publication No. 53-6113 (hereinafter referred to as "prior invention") discloses a unique method for preparing a hydrodesulfurization catalyst. That is, this method comprises (a) mixing powdery VIB Group and VIII Group metal compounds with refractory inorganic oxides to prepare an extrudable dough with a peptizer wherein the former two types of metal compounds are added in an amount corresponding to 60-90% by weight of the total amount of VIB Group and VIII Group metal compounds in the final catalyst product; (b) extruding the dough thus prepared and subjecting the extruded dough to drying and calcination; (c) impregnating the calcined extrudate with VIB Group and VIII Group metal compounds to form a final catalyst product containing 4-30% by weight (on the elementary basis) of VIB Group metal compound and 1-10% by weight (on the elementary basis) of VIII Group metal compound; and (d) subjecting the impregrated extrudate to drying and calcination in an oxidizing atmosphere to finally obtain a hydrodesulfurization catalyst. In short, according to the prior invention, catalyst metals are divided into two fractions. A larger amount of fraction is mixed with a catalyst carrier to form an extrudable dough and the remaining fraction is then added to the extrudate by impregnation. Although the cited reference discloses that the hydrodesulferization effect of this catalyst prepared by the above mentioned method is pretty good, but the result is not always satisfactory.